Electrochemical fuel cells facilitate chemical reactions between hydrogen and oxygen to generate electrical current. The chemical reactions take place in one or more membrane electrode assemblies (“MEA”). Each MEA typically includes an ion exchange membrane disposed between two electrodes, which are also referred to as gas diffusion layers. Between each electrode and the membrane is a catalyst, the location of which defines an electrochemically active area of the MEA.
One electrode functions as a cathode and the other electrode functions as an anode. Typically, hydrogen is supplied to the anode and oxygen is supplied to the cathode. The hydrogen and oxygen are directed to the electrodes in separate manifolds.
The membrane acts as a barrier to isolate the hydrogen and oxygen to prevent short-circuiting of the MEA. The membrane restricts passage of oxygen and hydrogen, but permits protons to pass between the anode and the cathode. In many MEA's, the membrane extends laterally beyond the perimeter of each electrode layer. Extending the membrane beyond the two electrodes helps to prevent passage of oxygen and hydrogen between the electrodes at the perimeter edges of the electrodes, which can short-circuit the MEA.
To further isolate the hydrogen and oxygen molecules, a gasket seal is provided around the perimeter edge of the electrodes and over the portion of the membrane that extends beyond the electrodes. To enhance the effectiveness of the seal, the seal is impregnated within the electrodes, which are typically porous and have a uniform density. The seal is made of an elastomeric material and can include multiple beads or protrusions to further increase the effectiveness of the seal.
In operation, hydrogen gas (H2) supplied to the anode reacts with the catalyst to split the H2 molecule into two H+ ions and two electrons. The electrons are conducted via the anode to an external circuit to provide current to the circuit that can be used for a variety of purposes, such as to power and turn a motor. The circuit next directs the electrons to the cathode side of the fuel cell.
Simultaneously, oxygen gas (O2) supplied to the cathode reacts with the catalyst to form two oxygen atoms. Each of the oxygen atoms have a strong negative charge. This negative charge attracts the H+ ions through the membrane. The H+ ions combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule (H2O).
A single MEA produces only a small voltage. To increase the amount of voltage produced, multiple MEAs are often combined in a fuel cell stack in a manner that is commonly known in the art. The multiple MEA's are typically separated by flow field plates, which are commonly referred to as separator plates.
While existing MEAs are suitable for their intended use, they are subject to improvement. For example, portions of the elastomeric seal sometimes enter the MEA active area during the manufacturing process as the elastomer is impregnated within the MEA. The presence of elastomer in the active area is undesirable because it restricts movement of gases and other particles in the active area, thereby decreasing the effective size of the active area and decreasing the efficiency of the fuel cell. Therefore, there is a need for a device and method that prevents portions of the seal from entering the active area during the impregnation process.
Existing MEA's also experience problems due to the size of the gasket seal or the distance that the seal extends above or below the MEA. For example, if the seal is too large and thus protrudes too far above or below the MEA then the seal will not properly fit between the MEA and the neighboring separator plates of a fuel cell stack. Further, such large seals exert more stress on the seal/MEA interlock than smaller seals due to numerous factors, such as their volume and increased exposure to outside forces that can highly strain the seal, thus making it more likely that larger seals, rather than smaller seals, will become detached from the MEA or damage the MEA. Still further, larger seals may permit more hydrogen permeation as compared to smaller seals. On the other hand, larger seals are more effective than smaller seals at preventing gross leakage from the MEA into the surrounding environment. Thus, there is a need for a seal that realizes the advantages associated with both large and small seals, while at the same time overcomes the disadvantages of each.